Air admittance vents (“AAVs”) are used in a variety of plumbing systems to prevent the escape of unwanted gases through drain pipes. AAVs are vertically connected to the drain pipes and supplement the vertical vent pipe in large plumbing systems. AAVs open under the vacuum created in the drain by the flow of water through the drain pipe and close when the water is no longer flowing through the drain.
Spring type AAVs, such as the plumbing vent valve described in U.S. Pat. No. 3,604,132, use a coil spring to hold the valve member closed. For many years, the spring type of AAVs were commonly used in the plumbing systems of recreational vehicles (“RVs”), as well as, in residential and commercial plumbing systems. The coil spring facilitated valving mechanism ensured that the vents remained closed while the RV moved even over rough roads. However, the introduction of a new United States industry standard, namely, NSF/ANSI 24 established by NSF International Standard/American National Standard and ASSE Standaard 1051 established by the American Society of Sanitary Engineering forced the use of spring-less, gravity type AAVs, such a the AAV described in U.S. Pat. No. 7,395,835. These industry standards required that the AAV open at extremely low pressure differentials, namely pressure differentials ranging from 0.009-1.0 psi. Even though ideal for use in RVs because the valve member was held closed by the coil spring even under rough travel conditions, conventional spring type AAVs could not be made to operated under the new standards. The coil springs that hold the valve closed and the flat valve seat generally prevent spring type AAVs from consistently opening at the very low pressure differentials imposed by the new standard. Various attempts were made to construct a springed AAV that would comply with the new standard, including the use of very light springs and valve elements, but were unsuccessful at balancing the holding force of the spring needed to keep the vent closed during rough travel conditions while still meeting the pressure differential standards.